Bootloader Host tool comes bundled with PSoC Creator installation. It can not run as a stand alone GUI.
If you don't want to install the complete version, you can extract the psoc_creator.exe and install PSoC_Creator_installer.msi. This msi installs the basic creator and does include the Host tool. I'm not sure if there is a plan to provide this tool independent of creator as users are likely to create their own tool !
Note: This msi installation doesn't not install the component libraries, example projects, compilers etc.
As far as I know,the USB Bootloader appnote has an equivalent tool,with source.
After receiving help from my customer base with VS 2015 programming (which I a far from knowledgeable about), attached is the complete source for a working stand alone bootloader host. It has been tested on a clean (only default installation) Windows 10 machine. NOTE: the Microsoft Visual C++ 2015 Redistributable (x86) must also be installed on the target host machine.
USBBootloaderHost_0.zip 704.5 K